JPH0739634B2 - Method for producing blackened and corrosion resistant hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention effectively suppresses the occurrence of black discoloration and white rust on a hot-dip galvanized steel sheet obtained by hot dipping pure zinc or a zinc alloy such as Zn-Al. The present invention relates to a method for producing a hot-dip galvanized steel sheet having excellent blackening resistance and corrosion resistance by performing the surface treatment.

In the present specification, pure zinc plating and zinc alloy plating are collectively called zinc alloy plating.

(Prior Art) Hot-dip galvanized steel sheets were called tin in the old days and were mainly used for building materials such as roofs and outer walls and daily sundries such as buckets. Has come to be used for. Further, hot-dip zinc alloy-plated steel sheets such as hot-dip Zn-Al alloy-plated steel sheets having further improved corrosion resistance have been developed.

These hot-dip galvanized steel sheets exhibit corrosion resistance by delaying the rust generation of the iron plate due to the sacrificial anticorrosion effect of Zn, but by performing chromate treatment after hot-dip Zn or Zn-Al alloy plating, the occurrence of rust is further prevented. It can be delayed to improve coating film adhesion. Due to its excellent corrosion resistance, the chromate-treated hot-dip galvanized steel sheet is used in automobiles, building materials, home appliances, and a wide range of other products that we see daily.

However, when the hot dip galvanized steel sheet is subjected to chromate treatment, if it is placed in a highly humid place for a long time during subsequent storage or after processing the target product, the so-called black discoloration phenomenon occurs. , The appearance is inferior and the commercial value is lost.

This black discoloration (also referred to as black rust) is characterized in that a particular crystallographic orientation in the spangle on the plating surface is particularly gray black, and therefore minimization of the spangle by a well-known method is also effective to some extent. In addition, there are Pb particles in the spangle where blackening occurs, and the presence of these Pb particles also promotes the occurrence of blackening, which is an extremely low Pb material (Pb0.
It is also known that black discoloration is less likely to occur in (01% or less). However, for hot-dip galvanized steel sheets, many users prefer spangle products, and it is unavoidable to add Pb to the plating bath. Furthermore, in the hot dip Zn-Al alloy plating, the Al concentration in the plating layer is high, and it is considered that blackening occurs due to the local cell action of Zn and Al. Under the circumstances described above, it is desired to solve the problem of black discoloration of hot-dip zinc and zinc alloy-plated steel sheets, and various methods have been proposed to prevent black discoloration.

JP-A-55-131178 discloses that a hot dip galvanized steel sheet is coated with a leveler or a skin pass roll after being lightly pressed for the purpose of shape correction, appearance improvement and mechanical property improvement. It is described that after heating, a chromate treatment is applied to prevent blackening. This method is to prevent the blackening by recovering the deteriorated plating surface by heating by heating, but it is not effective enough and requires equipment and energy for heating, which is economically disadvantageous. Is.

Japanese Unexamined Patent Publication (Kokai) No. 57-114695 describes a method of performing hot dip galvanizing, treating with an alkali metal carbonate-based solution to melt and remove oxides on the plating surface, and then performing electrogalvanizing. This method is to make the plating surface uniform and prevent blackening, and is a very effective method, but an electroplating line must be attached in addition to the hot dipping line, and the manufacturing equipment and process It becomes complicated and the cost is extremely high.

For the purpose of improving blackening resistance and corrosion resistance, it has also been proposed to treat a hot-dip galvanized steel sheet with an aqueous solution containing metal ions such as Ni, Co and Fe, and then subject it to chromate treatment. For example, in JP-A-59-177381, after hot dip galvanizing, the surface is treated with a solution containing Ni ions or Co ions or both to deposit Ni and / or Co on the plating surface, Then, a method of performing a chromate treatment is described.

In the method described in JP-A-61-110777, the hot dip galvanized steel sheet is washed with a Ni ion-containing alkaline aqueous solution,
Al in the plating surface layer is eluted and at the same time Ni is deposited on the surface, and then chromate treatment is performed.

Japanese Unexamined Patent Publication (Kokai) No. 62-20881 discloses a method in which after hot dip galvanizing, treatment is immediately performed with an alkaline aqueous solution containing both Fe ions and Ni ions to deposit Fe and Ni on the surface, followed by chromate treatment. Is listed.

The mechanism of blackening prevention by these methods is that the active Zn surface exposed on the plating surface by skin pass etc.
It is considered that the coating is performed by the precipitation of the substitution reaction of i, Co, etc., and as a result, the corrosion due to the local cell action due to Zn is suppressed and the blackening is prevented. Further, when an alkaline aqueous solution is used, it is considered that Al on the plating surface layer is removed by the alkali, which also contributes to blackening prevention. However, none of the above methods was able to sufficiently prevent blackening of the galvanized steel sheet. In particular, when the treatment is performed after mechanical processing such as skin pass, the plating surface is already smooth, so the adhesion between the metal coating such as Ni and Co deposited by the substitution reaction with weak bonding force and the plating surface is sufficient. Therefore, it was confirmed that the deposited metal and the chromate film were easily removed during the subsequent coiling and press working, resulting in local darkening (blackening).

(Problems to be Solved by the Invention) An object of the present invention is to perform a surface treatment capable of imparting the blackening resistance improved from the conventional one without impairing the corrosion resistance, and thereby the melting excellent in the blackening resistance and the corrosion resistance is achieved. It is to provide a method for producing a zinc-based plated steel sheet.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned objects, the present inventors have shown that treatment with an alkaline aqueous solution containing a small amount of Ni and / or Co ions and a specific amine compound, The present invention has been completed, knowing that a chromate treatment, particularly an acetic acid-containing chromate treatment, can provide a hot-dip galvanized steel sheet excellent in blackening resistance and corrosion resistance. The hot-dip galvanized steel sheet produced by the method of the present invention exhibits superior blackening resistance to the conventional one, and not only in the flat plate portion, but also in the portion subjected to ironing during slipping or pressing during coiling depending on processing conditions. It is possible to maintain resistance to blackening.

Here, the gist of the present invention is to provide a hot-dip zinc or zinc alloy plated steel sheet with 0.01 to 2.5% by weight of at least one metal ion selected from Ni and Co, C _{2 to} C ₁₂ alkylenediamine, and C ₂ to C. ₁₀ polyalkylene polyamine, and C ₂ -C ₁₀
After treatment with an aqueous solution containing at least one amine compound 0.05% by weight or more selected from alkanolamines and having a pH of 10 to 14, chromate treatment, preferably acetic acid 0.1 to
A method for producing a hot dip galvanized steel sheet having excellent blackening resistance and corrosion resistance, which comprises performing a chromate treatment with an acetic acid-containing chromate solution containing 5% by weight, chromic acid, and 0.1 to 10% by weight.

(Operation) Hereinafter, the present invention will be described more specifically. In the following description,% means% by weight unless otherwise specified.

The hot-dip galvanized steel sheet used in the method of the present invention is a normal hot-dip galvanized steel sheet, that is, Al: 0.08 to 0.20% and P
b: 0.2% or less, a galvanized steel sheet produced from a hot-dip galvanizing bath containing the balance Zn, and a hot-dip galvanized steel sheet such as a Zn-Al alloy-plated steel sheet may be used. A typical example of hot-dip Zn-Al alloy plated steel sheet is Al: 0.3 to 6.
Low Al Zn-Al alloy plated steel sheet produced from hot dip bath consisting of 0%, trace amounts of elements such as La, Ce, Mg, Si, etc., and Zn, and Al: 55%, Pb: 17%, Zn remaining. Is a high Al Zn-Al alloy plated steel sheet manufactured from a hot dip bath.

As described above, hot-dip galvanized steel sheets and hot-dip Zn-Al alloy-plated steel sheets of Pb-containing spangles or zero or minimum spangles have a strong blackening tendency, and thus the method of the present invention is applied to such plated steel sheets. A particularly remarkable blackening prevention effect is recognized. Similarly, the present invention may be carried out using other hot dip galvanized steel sheets.

The method of the present invention is applied to hot dip galvanized steel sheet with Ni and / or
Alternatively, treatment with an alkaline aqueous solution containing a specific polyamine or alkanolamine together with Co ions (hereinafter, this treatment is also referred to as pretreatment) and chromate treatment, particularly treatment with an acetic acid-containing chromate solution (hereinafter, this chromate treatment is also referred to as posttreatment). And) are sequentially applied.

Since the present inventors contain Pb, hot-dip galvanized steel sheets with spangles and zero spangle surfaces that easily cause blackening, 5% Al-Zn plated steel sheets as low Al alloy plated steel sheets,
And 55% Al-Zn plated steel sheet was used as the high Al alloy plated steel sheet, and the additive effective for preventing black discoloration was examined by the combination of the alkaline pretreatment liquid and the chromate-based post treatment as in the past. . As a result, in any of the hot-dip galvanized steel sheets, the alkaline aqueous solution used for the pretreatment was a metal ion composed of Ni, Co or both, and at least one selected from alkylenediamine, polyalkylenepolyamine and alkanolamine. It has been found that the black discoloration can be remarkably prevented when it contains an amine compound.

The amine compounds used in the surface treatment liquid for pretreatment in the present invention are C _{2 to} C ₁₂ alkylenediamine, C _{2 to} C ₁₀ polyalkylenepolyamine and C _{2 to} C ₁₀ alkanolamine. As specific examples of useful amine compounds, examples of alkylenediamine are ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7- Diaminoheptane,
1,8-diaminooctane, 1,9-diaminononane, 1,10-
Diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, etc .; examples of polyalkylene polyamines are diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc .; examples of alkanolamines Examples include monoethanolamine, diethanolamine and triethanolamine. These amine compounds may be used alone or in combination of two or more.

In the alkaline aqueous solution used for pretreatment in the present invention, the presence of such an amine compound is indispensable, and it has been proposed in the prior art to add it as a complexing agent to an alkaline surface treatment solution containing Ni or Co. Other organic compounds, such as ammonia, ethylenediaminetetraacetic acid, nitrilotriacetic acid, glycol etherdiaminetetraacetic acid, diethylenetriaminepentaacetic acid, which are typical complexing agents, in combination with Ni and / or Co In some cases, the blackening resistance is not substantially improved, and the aqueous solution may become unstable to form a precipitate. Not only that, also when these are used in combination with the amine compound used in the present invention, a decrease in blackening resistance may be observed. Therefore, in the alkaline surface treatment liquid used in the present invention, the additive is preferably only the amine compound.

In the surface treatment liquid for pretreatment, this amine compound was 0.
It is contained in an amount of 05% or more, preferably 0.1% or more. If the content of the amine compound is less than 0.05%, the solubility of Ni and Co ions deteriorates, the deposition of these metals on the plating surface is insufficient, and blackening cannot be sufficiently prevented. The upper limit of the content of the amine compound is not particularly limited because the amine compound does not have an adverse effect even if it is present in excess. When two or more amine compounds are used together, the total amount is 0.05%
Try to be above.

The metal ions present in the alkaline aqueous solution for pretreatment are
Ni, Co or both, other metal ions nobler than Zn, for example, Cu, Ti, Fe, Sn, Mn, etc., blackening resistance in the presence of an alkaline aqueous solution in combination with the amine compound. No improvement can be obtained. Therefore, it is preferable that the alkaline aqueous solution used for pretreatment in the present invention does not substantially contain metal ions other than Ni and Co.

The metal ion selected from Ni and Co is present in the alkaline aqueous solution of the present invention at a concentration of 0.01 to 2.5% (the total concentration when both Ni and Co coexist). If it is less than 0.01%, the effect of preventing black discoloration cannot be sufficiently obtained. On the other hand, if the concentration of these metal ions exceeds 2.5%, the corrosion resistance deteriorates,
White rust tends to occur.

Ni and / or Co ions are added to an alkaline aqueous solution as various salts or oxides or hydroxides. Examples of salts that may be used are chlorides, nitrates, sulphates,
Examples include phosphates, acetates, oxalates and the like.

The pH of the surface treatment solution for pretreatment is 10-14. PH of aqueous solution
When is less than 10, blackening resistance is poor. A particularly preferred pH range is 10 to 13.5. If necessary, the pH of the aqueous solution is adjusted to 10 to 14 by adding any alkaline inorganic substance that does not adversely affect the performance of the surface treatment solution. The pH is usually adjusted by the addition of alkali metal hydroxides such as sodium and potassium hydroxide. However, in the present invention, since a basic amine compound is used as an additive, depending on the type and amount of the amine additive, the pH of the aqueous solution may be maintained at 10 or more without such pH adjustment. is there.

This alkaline surface treatment liquid for pretreatment is applied to the hot dip galvanized steel sheet by an appropriate method such as spraying or dipping. The treatment time may be as short as about 1 second to several tens of seconds, whereby Ni and / or Co metal is deposited on the plating surface. Precipitation amount of Ni and / or Co on the plated surface is preferably in the range of per side 0.1 to 30 mg / m ² in terms of metal, and more preferably in the range of 0.5 to 10 mg / m ^2. Ni
When both and Co are used together, the total amount of both should be within this range. If this adhesion amount is insufficient, the blackening resistance is not sufficiently improved, while if it is too large, the corrosion resistance tends to decrease, and the steel sheet becomes dark and the commercial value decreases.

The mechanism of blackening prevention by this pretreatment is the conventionally known Ni
And / or essentially the same as with a Co-containing alkaline aqueous solution, ie, Al on the surface layer due to alkali
It is thought that this is due to the elution of the metal and the precipitation of the above-mentioned metal, but in the case of the treatment liquid of the present invention, the addition of the amine compound may cause the deposited metal to adhere more strongly to the plated surface than the conventional surface treatment liquid. Be done.

The temperature condition of this treatment is not particularly limited. That is, the hot dip galvanized steel sheet to be treated is at room temperature, or
A high temperature up to about 350 ° C may be used. Therefore, it is possible to apply the surface treatment solution to the zinc-based plated steel sheet immediately after hot dipping while still at a high temperature. The temperature of the alkaline surface treatment liquid may be room temperature to 100 ° C. However, in order to shorten the treatment time, it is more preferable that at least one of the steel plate temperature and the treatment liquid temperature is 50 ° C. or higher. If necessary, heat drying is performed after the surface treatment.

After performing the pretreatment as described above, the chromate treatment is performed. This chromate treatment contains a conventionally used chromate solution, that is, chromic anhydride, and if necessary, a suitable fluorine-containing compound (eg, hydrofluoric acid, sodium silicohydrofluoride, etc.) and Alternatively, an inorganic acid (eg, phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, etc.), or an aqueous solution containing a silicon compound (silica sol, colloidal silica, organic silicate, etc.) may be added, but acetic acid and chromic acid are preferable. Is carried out using a chromate solution containing acetic acid.

By using an acetic acid-containing chromate solution, it is possible to obtain hot-dip galvanized steel sheets with improved blackening resistance and corrosion resistance. The generation of rust can be suppressed. This is because Zn or acetic acid in the chromate solution
It is considered that aluminum acetate is generated by reacting with Al on the surface of the Zn-Al alloy plating film, and this aluminum acetate is effective in preventing black discoloration and white rust. In order to sufficiently exert this effect, it is preferable to use a chromate solution having a chromic acid concentration of 0.1% or more and an acetic acid concentration of 0.1% or more. On the other hand, if the concentrations of chromic acid and acetic acid are too high, the surface of the steel sheet becomes yellowish, which lowers the commercial value. This phenomenon occurs when the chromic acid concentration is 10
%, And when the acetic acid concentration exceeds 5%, it becomes remarkable. Therefore,
When using a chromate solution containing acetic acid, the chromic acid concentration is
It is preferable that the concentration is 0.1 to 10%, particularly 0.3 to 3.0%, and the acetic acid concentration is 0.1 to 5%, particularly 0.5 to 3.5%.

A part of chromium in the chromate solution may be a water-soluble trivalent chromium compound in order to promote the formation of a chromate film. Further, this chromate solution can be used as a coating type chromate solution by containing silica sol.

The chromate treatment performed as a post-treatment in the present invention can be carried out in the same manner as a normal chromate treatment. That is, the treatment can be carried out at room temperature or at a slightly high temperature by an appropriate means such as dipping, coating or spraying. The treatment time is about several seconds to 10 minutes, which is usually 10 seconds or less for the coating type and longer than that for the reaction type. Coating weight of the chromate film is in the range of per side 1 to 100 mg / m ² of Cr metal basis, especially in the range of 5-60 mg / m ² is preferred. After the chromate treatment, if necessary, heat drying is performed to dry the chromate film.

Next, the present invention will be described in more detail with reference to examples.

The hot-dip galvanized steel sheets used in the examples are the following four types (all double-sided steel sheets). The base steel sheets were all low carbon cold-rolled steel sheets with a thickness of 1.0 mm.

Steel plate 1: spangle Zn manufactured by continuous hot-dip Zn plating line
Galvanized steel sheet Plating bath composition Al: 0.05%, Pb: 0.010%, Fe: 0.02 to 0.03%, rest Zn plating bath temperature 470 ℃ Line speed 100m / min Zn adhesion amount 270g / m ² (one side amount) Skin pass elongation 1.0% Post-treatment No chromate treatment Steel plate 2: Zero spangle Zn-plated steel plate produced by continuous hot-dip Zn plating line Plating bath composition Al: 0.15%, Pb: 0.10%, Fe: 0.02-0.03%, Remaining Zn plating bath temperature 470 ° C Line speed 100m / min Zn adhesion amount 270g / m ² (one side amount) Skin pass elongation 1.0% Post-treatment without chromate treatment Steel plate 3: 5% Al-Zn alloy plated steel plate manufactured by continuous hot-dip Zn plating line Plating bath composition Al: 5% , Pb: 0.01% or less, Fe: 0.02% or less, misch metal: 0.06
%, Remaining Zn plating bath temperature 460 ℃ Line speed 70m / min Coating weight 90g / m ² (one side amount) Skin pass elongation 0.8% Post-treatment without chromate treatment Steel plate 4: 55% Al produced by hot dip plating in the laboratory −Zn
Alloy-plated steel sheet Plating bath composition Al: 55%, Si: 1.7% or less, remaining Zn plating bath temperature 600 ° C Coating weight 175g / m ² (one-side amount) Skin pass elongation 0.8% Post-treatment No chromate treatment Example 1 Implementation The example shows the effect of the type of non-metal additive added to the pretreatment liquid on blackening resistance and corrosion resistance.

Using the above-mentioned four types of hot-dip galvanized steel sheet test materials, treatment with a pretreatment liquid and subsequent chromate treatment were carried out as follows.

The alkaline aqueous solution used for pretreatment was Ni ²⁺ of 0.
Aqueous solution containing 05% NiCl ₂ and 2.5% various organic amines or other organic or inorganic compounds and adjusted to pH 13 with sodium hydroxide.

As a chromate solution, 1.0% acetic acid and 5% chromic acid
An aqueous solution containing was used.

First, each sample steel sheet at room temperature was sprayed with the above alkaline aqueous solution at a liquid temperature of 20 ° C. for 10 seconds to pretreat the plated steel sheet. Then, after washing with water and draining, a chromate treatment was carried out by immersing in the above-mentioned acetic acid-containing chromate solution at room temperature for 1 minute, and after draining, it was dried at 60 ° C. for 10 minutes to form a chromate film. After that, the obtained surface-treated plated steel sheet was stored in a desiccator at room temperature for 7 days, and then tested for blackening resistance in the following manner.

Blackening resistance test: A test piece was wrapped in white clay kneaded with water, put in a nylon bag, immersed in warm water at 80 ° C for 24 hours, and then taken out to visually determine the occurrence of blackening.

The test results were evaluated according to the following criteria.

◯: Good (no black discoloration) Δ: Slightly good (black discoloration, area ratio less than 40%) ×: Poor (black discoloration, area ratio 40% or more) In addition, each prepared alkaline treatment liquid was kept at room temperature for 7 days. After standing for one day, the stability of the treated aqueous solution was judged by the following criteria by visually observing the solution.

◯: Stable (no precipitate was observed) Δ: Slight precipitate was formed X: Precipitate was formed.

The test results are shown in Table 1 below. Among the additives used in Table 1, the compounds marked with * are amine compounds used in the present invention. In addition, Table 1 shows the results when the test steel plate is steel plate 3 (5% Al-Zn alloy plated steel plate), but the test results are the same when other hot dip galvanized steel plates are used. It was confirmed that the tendency was shown.

From the results shown in Table 1, it is understood that the occurrence of blackening is effectively suppressed and the treatment liquid is stably maintained only when the amine compound of the present invention is added to the alkaline aqueous solution for pretreatment. Unexpectedly, the stability of the solution is good when adding ethylenediaminetetraacetic acid or nitrilotriacetic acid, which are commonly used as complexing agents to keep Ni in a stable state in an alkaline aqueous solution. However, the effect of suppressing the occurrence of blackening was not observed.

Example 2 The same experiment as in Example 1 was repeated. However, the test steel plate is steel plate No. 3, and the alkaline aqueous solution for pretreatment contains
Various metal chlorides were used in place of NiCl _2, and triethylenetetramine was used as an organic additive. The amount of metal chloride added was 0.05% in terms of metal, the amount of triethylenetetramine added was 2.5%, and the pH of the solution was adjusted to 13 with sodium hydroxide. The other conditions were the same as in Example 1, and the blackening resistance of the obtained surface-treated plated steel sheet was determined in the same manner as in Example 1. The results are shown in Table 2 below.

From the results shown in Table 2, it can be seen that when the metals are Ni and Co, an excellent effect of preventing blackening is obtained, and with other metals, blackening is not prevented.

Example 3 The same experiment as in Example 1 was repeated. However, the test steel plate is steel plate No. 3, and the alkaline aqueous solution for pretreatment contains
Ni and Co chlorides as metal compounds and ethylenediamine or ethylenediaminetetraacetic acid as an additive were added. The addition amount is 0.05% for Ni and Co, and 2.5 for ethylenediamine and ethylenediaminetetraacetic acid, respectively.
% And the pH was adjusted to 10 or 13 with sodium hydroxide. The surface-treated plated steel sheet thus obtained was evaluated for white rust resistance as well as blackening resistance according to the following procedure.

White rust resistance test: A salt spray test at 35 ° C on the test piece
After 120 hours, the occurrence of white rust was visually observed.
The results are the same criteria as in the blackening resistance test, 3 of ○, △, ×
It was judged in stages.

From Table 3, the same tendency as in Tables 1 and 2 can be seen. That is, when the alkaline treatment liquid for pretreatment contains Ni and / or Co and ethylenediamine which is the amine compound of the present invention, the blackening resistance is improved, whereas the organic compound is changed to ethylenediaminetetraacetic acid. Then, this improvement cannot be obtained. Although only the acetic acid-containing chromate treatment improves the white rust resistance, it cannot prevent the occurrence of blackening.

Example 4 For pretreatment by adding 0.01% (as Ni ²⁺ , as Co ₂₊ ) NiCl ₂ , CoCl ₂ and various amounts of ethylenediamine to water and adjusting the pH to 13 with sodium hydroxide. An alkaline aqueous solution was obtained. The stability of this solution was evaluated by the same method as in Example 1. The results are shown in Table 4 below.

When 0.05% or more of amine compound was added, Ni and Co could be stably maintained in a solution state.

Example 5 Melt in the same manner as in Example 1 except that ethylenediamine was added as an additive in an amount of 2.5% and various amounts of NiCl ₂ and CoCl ₂ were added as metal compounds to an alkaline aqueous solution for pretreatment. The zinc-plated steel sheet (test steel sheet No. 2) was surface-treated. After the acetic acid-containing chromate treatment, the plated steel sheet was tested for blackening resistance as in Example 1. The test results are shown in Table 5 below.

To prevent blackening, at least 0.01% Ni ²⁺ , Co
^It can be seen that it is necessary to include ²⁺ in the pretreatment liquid.

Example 6 As an alkaline aqueous solution for pretreatment, a solution containing an amine compound or other additives in addition to Ni, Co or both compounds was used, and a hot dip galvanized steel sheet was surfaced in the same manner as in Example 1. Processed.

The plated steel sheet used in this example is steel sheet 3 (5%
It is an Al-Zn alloy plated steel sheet, and the pretreatment is to coat the plated steel sheet at room temperature with an alkaline aqueous solution (NaOH or KO) at a liquid temperature of 60 ° C.
The pH was adjusted to 13 with H) for 2 seconds, and the subsequent processing operation was the same as in Example 1.
The surface-treated plated steel sheet obtained after the chromate treatment was allowed to stand in a desiccator at room temperature for 7 days, and then blackening resistance and corrosion resistance (white rust resistance) were evaluated in the same manner as above. The results are summarized in Table 6 below together with the types of additives.

As can be seen from the results in Table 6, in the examples of the present invention using the surface treatment liquid containing the amine compound used in the method of the present invention, blackening was effectively prevented, and white rust was suppressed. Within the scope of the present invention, when using Ni and Co together,
Alternatively, when a metal compound other than chloride was used, and also when the pH was adjusted with KOH, the same excellent effect as in the above-mentioned Examples was obtained. However, if an additive out of the range of the present invention is used as the additive, or if the amount of the metal species added is out of the range of the present invention, black discoloration and white rust cannot be suppressed simultaneously. That is, if the added amount of the metal species (Ni, Co) is less than 0.01%, the effect of improving the blackening resistance is not recognized, and if the added amount exceeds 2.5%, the corrosion resistance (white rust resistance) deteriorates.

Example 7 As Example 6, except that an alkaline aqueous solution containing NiCl ₂ at a Ni ²⁺ concentration of 0.05% and 2.5% triethanolamine was used as the alkaline aqueous solution for pretreatment. The test material of Steel plate 3 was surface-treated. The pH was adjusted with NaOH. After acetic acid-containing chromate treatment, blackening resistance and corrosion resistance were tested as in the previous examples. The results are shown in Table 7 below.

From the results shown in Table 7, it can be seen that the effect of preventing blackening cannot be obtained when the pH is lower than 10. When the pH was close to 14, the corrosion resistance was slightly deteriorated.

Example 8 The surface treatment described in Example 1 was repeated. However, the pretreatment was carried out on the test material of steel plate 3 at a temperature of 150 ° C with a C ²⁺ concentration of 0.05%.
It was carried out by spraying an aqueous solution of pH 13 containing oCl ₂ and 2.5% ethylenediamine (temperature 70 ° C.) for 2 seconds, and the post-treatment chromate solution was 0.1% acetic acid and 5%.
It was carried out using an acetic acid-containing chromate solution containing 1% chromic acid or a conventional chromate solution. The composition of the conventional chromate solution used was 3% chromic acid, 0.3% phosphoric acid,
It was 0.1% of hydrofluoric acid. The resulting surface-treated steel sheet was tested for blackening resistance and white rust resistance by the same method as described above. However, in this example, not only the flat plate portion of the test piece,
Blackening resistance and white rust resistance are also obtained for the rubbed part of the plate (the rubbed part when two test pieces are rubbed manually) and the press squeezing part (the squeezing part on the side wall of the square tube diaphragm). It tested similarly. The test results are shown in Table 8 below.

As can be seen from the results in Table 8, when the conventional chromate solution was used for the post-treatment, the flat plate portion had sufficient blackening resistance and white rust resistance, and some improvement effects were obtained.
The black discoloration resistance was particularly reduced in the plate rubbed portion and the pressed and ironed portion. On the other hand, when the acetic acid-containing chromate solution was used, the blackening resistance was improved in the plate rubbing part and the press ironing part as in the flat plate part.

Example 9 Using each test steel sheet of hot dip galvanized steel sheets 1 to 4,
The surface treatment was carried out in the same manner as in Example 1. The alkaline processing liquid is obtained by adjusting the pH10 by NoOH an aqueous solution containing an amount of NiCl ₂ and 2.5% of ethylenediamine Ni ²⁺ concentration of 0.05%, a solution temperature alkaline solution treatment is by spraying for 2 seconds and steel The temperature was varied. Then, using an acetic acid-containing chromate solution containing 0.1% acetic acid and 5% chromic acid or a conventional chromate solution (the composition is the same as that used in Example 8), at room temperature.
Chromate treatment was performed by immersion treatment for 10 seconds.

For comparison, a test piece was prepared by omitting the treatment with the alkaline aqueous solution and performing only the treatment with the acetic acid-containing chromate solution or the conventional chromate solution.

Using the test pieces of these surface-treated steel sheets, blackening resistance and white rust resistance were evaluated by the same method as described above. However, in this example, not only the flat plate portion of the test piece but also the example 8 was used.
Similarly, the blackening resistance and the white rust resistance of the rubbed portion and the pressed and ironed portion of the plate were evaluated. The test results are shown in Table 9 below.

From the results shown in Table 9, it is possible to obtain sufficient blackening resistance and corrosion resistance not only in the flat plate portion but also in the plate rubbing portion and the press ironing portion by the method of the present invention even when the treatment conditions with the alkaline treatment liquid are changed. I understand. On the other hand, when pretreatment with an alkaline treatment liquid is not performed, it is effective only in preventing white rust on the flat plate portion, blackening resistance is not obtained at all, and white rust resistance is Is insufficient.

(Effects of the Invention) By the method of the present invention, it is possible to produce a plated steel sheet that does not cause the problem of blackening without impairing the corrosion resistance of the zinc-based plated steel sheet. In particular, when the post-treatment is performed using an acetic acid-containing chromate solution, sufficient blackening resistance and corrosion resistance can be maintained even in a frictional portion such as a plate rubbing portion and a press ironing portion. Moreover, in the treatment with the alkaline aqueous solution performed prior to the chromate treatment, the amount of the metal species and the amine compound used may be very small, which is economically advantageous, and the treatment can also be carried out by a simple method such as spraying or dipping, It is easy to modify the device. Therefore, the method of the present invention is very practical and contributes greatly to the improvement of the quality of the hot-dip galvanized coating and the expansion of its applications.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naotaka Ueda, 1850 Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Steel Works (72) Inventor, Shunichi Maru 4-1-2, Kagino-nishi, Joto-ku, Osaka, Osaka No. Asahi Kagaku Kogyo Co., Ltd. (72) Inventor Toshio Kiya 4-124, Kagino Nishi, Joto-ku, Osaka City, Osaka Asahi Kagaku Kogyo Co., Ltd.

Claims (2)

[Claims] 1. A hot dip galvanized or zinc alloy plated steel sheet is plated with Ni.
And at least one metal ion selected from Co 0.01
2.5 wt% and, C ₂ -C ₁₂ alkylene diamine, C ₂ -C ₁₀
At least one amine compound selected from polyalkylene polyamines and C _{2 to} C ₁₀ alkanolamines.
A method for producing a hot-dip galvanized steel sheet having excellent blackening resistance and corrosion resistance, which is characterized by performing a chromate treatment after treatment with an aqueous solution containing 05% by weight or more and having a pH of 10 to 14. 2. The method according to claim 1, wherein the chromate treatment is performed with an acetic acid-containing chromate solution containing 0.1 to 5% by weight of acetic acid and 0.1 to 10% by weight of chromic acid.